An essential part of each coin-operated telephone is apparatus responsive to the deposit of a coin for generating signals indicative of the value of the deposit. In one prior art coin telephone, each deposited coin strikes a distinctive gong or chime. The sound generated thereby is converted to an electrical signal by means of a transducer and then applied to the telephone line. The operator then interprets the sounds and thereby determines the particular coin deposited.
In another prior art coin-operated telephone station, a switching device is included which operates one or more times in response to the deposit of each coin. Each switch operation is indicative of an incremental coin value such as 5 cents. Each operation of the switch energizes an oscillator that generates an electrical signal burst in the audible frequency range. The bursts are counted by the operator to determine the value of the coin deposited. A system of this type is disclosed in E. R. Andregg et al. U.S. Pat. No. 3,146,312, issued Aug. 25, 1964.
Operators working with the above-described coin identification systems are sometimes confused as to whether signals generated at a TOUCH-TONE.RTM. signal dial are dial signals or coin deposit signals. Unfortunately, certain telephone users attempt to fool the operator into thinking that the requisite coins have been deposited by depressing certain combinations of the pushbuttons to generate series of tones.
J. E. Edington U.S. Pat. No. 3,428,751, issued Feb. 18, 1969, discloses one arrangement that allows the operator to distinguish dialed tones from coin deposit signals. In the Edington arrangement, a distinctive single frequency guard tone is provided at the termination of each dialed signal. Thus if an operator hears this guard tone, he or she then realizes that the preceding tone was generated from the pushbuttons rather than from the deposit of coins. The Edington arrangement appears to be effective in preventing the use of a TOUCH-TONE signaling dial to generate coin deposit signals. However, it is ineffectual in regard to coin deposit signals produced by tape recorders, tone generators or similar devices which signals are entered into the receiver of the coin station to obtain free telephone service.
It is an object of this invention to prevent the fraudulent generation of coin deposit signals.
It is a further object of this invention to provide a mechanism of automating the detection of coin deposit signals to help an operator or automated call-processing system differentiate between valid and invalid coin deposit signals.